Method to manufacture paper

ABSTRACT

The present invention relates to a paper or paperboard substrate containing fiber-filler complexes as well as methods of making and using the same.

FIELD OF THE INVENTION

The present invention relates to a paper or paperboard substrate containing fiber-filler complexes as well as methods of making and using the same.

BACKGROUND OF THE INVENTION

Inorganic material such as precipitated calcium carbonate (PCC) ground calcium carbonate (GCC), clay and talc are used extensively as fillers in the paper making process. Filler loading levels of 12-25wt % are typical in current paper making strategy to improve optical properties of the paper such as brightness and opacity. In some instances, the economics of substituting expensive fiber with inexpensive filler lends added incentive.

To insure that the fillers remain with the fiber web and ultimately with the paper product, retention aids are used. Normally retention aids are long chained polymeric compounds that flocculate the furnish and enhance filler-fiber “attachment.” However, high flocculation levels, caused in part by retention aids, lead to non-uniformity in the web and poor paper formation.

To circumvent this, a method to attach the filler directly on to the fiber surfaces was described in French Patent 92-04474 and U.S. Pat. Nos. 5,731,080 & 5,824,364 to Cousin et al which are hereby incorporated in their entirety by reference. In these patents a slip stream of pulp furnish is refined to low freeness (<70 Canadian standard freeness [csf] vs. 450 csf, typically) and then treated to generate a highly loaded filler-fiber complex. When these complexes are recombined with untreated pulp, any desirable filler level can be targeted.

An alternative approach is described in U.S. Pat. No. 5,679,220 to Matthew et al. and U.S. Pat. No. 5,665,205 to Srivatsa et al which are hereby incorporated in their entirety by reference. In both Srivatsa and Matthew the entire furnish is treated to nominal filler loadings without subjecting the pulp to high refining levels (low freeness). However, this procedure results in increases in capital and operating costs due to the treatment of larger pulp volumes. Accordingly, there is a need in the art to generate filler-fiber complexes easily and inexpensively.

It is known in the art to produce fiber-filler complexes by contacting a fiber slurry with slaked lime and carbon dioxide gas to precipitate calcium carbonate (PCC). Such processes are described in the Cousin et al., Srivatsa, and Matthew et al. patents. The Cousin et al. patents describe a process for obtaining a fiber-based composite produced by precipitating calcium carbonate in situ in an aqueous suspension of fibers of expanded surface area having microfibrils on their surface. The crystals of precipitated calcium carbonate (PCC) are organized essentially in clusters of granules directly grafted on to the microfibrils without any binders or retention aids such that the crystals trap the microfibrils by reliable and non-labile bonding. Srivatsa et al. describes in situ precipitation on secondary fiber furnish. Whereas the Cousin et al. patents describe a batch reaction process, Matthew et al. describes a continuous process for forming fiber-filler complexes.

Typically, as you refine pulp, more surface area is generated and additional anchoring sites are created on the fiber. However, U.S. Pat. No. 6,592,712, which is hereby incorporated, in its entirety, herein by reference, provides a source of fiber having a high surface area without the need for additional refining by obtaining them from process streams within the paper making process. However, the internally recirculated high surface area fiber stream containing the recirculated fibers, also known as “fines”, used is quite variable because it contains residuals of unretained filler and other papermaking materials such as sizing agents, optical brightening agents in addition to dyes and pigments. These chemicals can lead to problems in their subsequent use, such as quenching of residual sizing and OBAs when exposed to the high pH environments such as those required during the start of PCC formation. In addition, the utilization of the highly variable streams containing the “fines” can lead to problems with uniformity within a paper substrate made therefrom.

SUMMARY OF THE INVENTION

One aspect of the present invention is a paper substrate, containing a plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average and having a filler attached thereto a portion of said plurality and also containing less than 50wt % fibers that are less than 75 μm in length on average based upon the total weight of the substrate. The fibers that are hardwood species, softwood species or mixtures thereof may have a Canadian Standard Freeness of from 300 to 600 and may be virgin fibers. The fibers that are less than 75 μm in length on average may be recycled fibers, recirculated fibers, waste fibers, or mixtures thereof. The fibers that are less than 75 μm in length may be present in an amount that is from 0.1 to 20 wt % based upon the total weight of the substrate.

Another aspect of the present invention is a paper substrate, containing a plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average and having a filler attached thereto a portion of said plurality and also containing less than 50 wt % fibers that are less than 75 μm in length on average based upon the total weight of the substrate where the filler is present in an amount of from 1 to 30 wt % based upon the total weight of the substrate. The filler may be attached at a filler to fiber weight ratio of from 0.3 to 8. The filler may be precipitated. Further, the filler may be precipitated calcium carbonate. The filler may be in at least one shape of selected from the group consisting of cubic, scalenohdral, rhombic, and aragonite. The filler has an average particle size of from 0.01 to 20

Another aspect of the present invention is a method of making a paper substrate by contacting a plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average and having a filler attached thereto a portion of said plurality with fibers that are less than 75 μm in length on average based upon the total weight of the substrate.

Another aspect of the present invention is a method of making a paper substrate by contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially.

Another aspect of the present invention is a method of making a paper substrate by contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average in-line with Ca(OH)₂ to form a slurry having less than 5% solids.

Another aspect of the present invention is a method of making a paper substrate by contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with CO₂ gas prior to contacting the plurality of fibers with Ca(OH)₂.

Another aspect of the present invention is a method of making a paper substrate by contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with CO₂ gas prior to contacting the plurality of fibers with Ca(OH)₂.

Another aspect of the present invention is a method of making a paper substrate by contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially at a pH of from 7.5 to 11.

Another aspect of the present invention is a method of making a paper substrate by contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially in a tubular reactor, wherein CO₂ is added to the reactor at multiple addition points.

Another aspect of the present invention is a method of making a paper substrate by contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially in a series of continuous stirring tank reactor, wherein CO₂ is added to each of the continuous stirring tank reactor in the series.

Another aspect of the present invention is a method of making a paper substrate by contacting both the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average and the fibers that are less than 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially in a series of continuous stirring tank reactor, wherein CO₂ is added to each of the continuous stirring tank reactor in the series.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: A plot of Sheffield smoothness, in Sheffield Units (SU), of the ID side of a paper substrate versus the wt % ash contained in that paper substrate.

FIG. 2: A plot of Sheffield smoothness, in Sheffield Units (SU), of the NS side of a paper substrate versus the wt % ash contained in that paper substrate.

FIG. 3: A table comparing the fluorescence of the residual OBA from a SaveAll fiber fine stream sample before and after the sample is reacted to form the fiber fine-filler complex.

FIG. 4 is a schematic diagram of a process employing several of the features of the present invention.

FIG. 5 is a schematic representation of one embodiment of an apparatus for carrying out the process of the present invention.

FIG. 6 is a schematic representation of one embodiment of a process, combined with apparatti for carrying out the process of the present invention.

FIG. 7 is a schematic representation of one embodiment of a process to make a fiber-filler complex where a (plug flow) reactor is used and a series of CO₂ addition occur throughout the reactor.

FIG. 8 is a schematic representation of one embodiment of a process to make a fiber-filler process where multiple continuous stirring tank reactors are used in series.

FIG. 9 is paper substrate comparison as a function of precipitated filler morphology.

FIG. 10 is SEM showing morphology results of tubular reactor.

FIG. 11 is first SEM showing morphology results of CSTR reactor.

FIG. 12 is second SEM showing morphology results of CSTR reactor.

FIG. 13 is first SEM showing cubic morphology.

FIG. 14 is second SEM showing cubic morphology.

FIG. 15 is third SEM showing cubic morphology.

FIG. 16 is fourth SEM showing cubic morphology.

FIG. 17 is a plot of HST sizing vs % PCC.

FIG. 18 is a plot of Modulus vs % PCC.

FIG. 19 is a plot of internal bond vs % PCC.

FIG. 20 is a plot of GM breaking lenght vs % PCC.

FIG. 21 is a plot of GM Taber Stiffness vs % PCC.

FIG. 22 is a plot of Brightness with IW vs % PCC.

FIG. 23 is a plot of Brightness without UV vs % PCC.

FIG. 24 is a plot of Flourescence (delta Brightness) vs % PCC.

FIG. 25 is a very preferred embodiment of the process of making the fiber filler complex.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have discovered a method of making a paper or paperboard substrate containing fiber-filler complexes, as well as a method of making the same, that solves all of the above-mentioned problems identified while utilizing conventional paper substrates and methodologies.

The paper substrate contains a web of cellulose fibers. The paper substrate of the present invention may contain recycled fibers and/or virgin fibers. Recycled fibers differ from virgin fibers in that the fibers have gone through the drying process several times.

The paper substrate of the present invention may contain from 1 to 99 wt %, preferably from 5 to 95 wt %, most preferably from 60 to 80 wt % of cellulose fibers based upon the total weight of the substrate, including 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 99 wt %, and including any and all ranges and subranges therein.

Preferably, the sources of the cellulose fibers are from softwood and/or hardwood. The paper substrate of the present invention may contain from 1 to 99 wt %, preferably from 5 to 95 wt %, cellulose fibers originating from softwood species based upon the total amount of cellulose fibers in the paper substrate. This range includes 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 wt %, including any and all ranges and subranges therein, based upon the total amount of cellulose fibers in the paper substrate.

The paper substrate may alternatively or overlappingly contain from 0.01 to 100 wt % fibers from softwood species, preferably from 0.01 to 50 wt %, most preferably from 5 to 40 wt % based upon the total weight of the paper substrate. The paper substrate contains not more than 0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 wt % fines based upon the total weight of the paper substrate, including any and all ranges and subranges therein.

The paper substrate may contain softwood fibers from softwood species that have a Canadian Standard Freeness (csf) of from 300 to 700, more preferably from 250 to 650, most preferably from 400 to 550 csf. This range includes 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420,430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, and 550 csf, including any and all ranges and subranges therein.

The paper substrate of the present invention may contain from 1 to 99 wt %, preferably from 5 to 95 wt %, cellulose fibers originating from hardwood species based upon the total amount of cellulose fibers in the paper substrate. This range includes 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 wt %, including any and all ranges and subranges therein, based upon the total amount of cellulose fibers in the paper substrate.

The paper substrate may alternatively or overlappingly contain from 0.01 to 100 wt % fibers from hardwood species, preferably from 50 to 100 wt %, most preferably from 60 to 99 wt % based upon the total weight of the paper substrate. The paper substrate contains not more than 0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 99 and 100 wt % fines based upon the total weight of the paper substrate, including any and all ranges and subranges therein.

The paper substrate may contain softwood fibers from hardwood species that have a Canadian Standard Freeness (csf) of from 300 to 700, more preferably from 250 to 650, most preferably from 400 to 550 csf. This range includes 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, and 550 csf, including any and all ranges and subranges therein.

When the paper substrate contains both hardwood and softwood fibers, it is preferable that the hardwood/softwood ratio be from 0.001 to 1000. This range may include 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 including any and all ranges and subranges therein and well as any ranges and subranges therein the inverse of such ratios.

The hardwood and soft wood fibers are preferably not less than 75 μm in length on average, more preferably not less than 80 μm in length, most preferably not less than 100 μm in length. The length of these fibers are greater than or equal to 75, 77, 80, 82, 85, 87, 90, 92, 95, 97, an 100 μm in length, including any and all ranges and subranges therein and well as any ranges and subranges therein.

Further, the softwood and/or hardwood fibers contained by the paper substrate of the present invention may be modified by physical and/or chemical means. Examples of physical means include, but is not limited to, electromagnetic and mechanical means. Means for electrical modification include, but are not limited to, means involving contacting the fibers with an electromagnetic energy source such as light and/or electrical current. Means for mechanical modification include, but are not limited to, means involving contacting an inanimate object with the fibers. Examples of such inanimate objects include those with sharp and/or dull edges. Such means also involve, for example, cutting, kneading, pounding, impaling, etc means.

Examples of chemical means include, but is not limited to, conventional chemical fiber modification means including crosslinking and precipitation of complexes thereon. Examples of such modification of fibers may be, but is not limited to, those found in the following patents U.S. Pat. Nos. 6,592,717, 6,592,712, 6,582,557, 6,579,415, 6,579,414, 6,506,282, 6,471,824, 6,361,651, 6,146,494, H1, 704, U.S. Pat. Nos. 5,731,080, 5,698,688, 5,698,074, 5,667,637, 5,662,773, 5,531,728, 5,443,899, 5,360,420, 5,266,250, 5,209,953, 5,160,789, 5,049,235, 4,986,882, 4,496,427, 4,431,481,4,174,417, 4,166,894, 4,075,136, and 4,022,965, which are hereby incorporated, in their entirety, herein by reference.

Sources of “Fines” may be found in SaveAll fibers, recirculated streams, reject streams, waste fiber streams. The amount of “fines” present in the paper substrate can be modified by tailoring the rate at which such streams are added to the paper making process.

The paper substrate preferably contains a combination of hardwood fibers, softwood fibers and “fines” fibers. “Fines” fibers are, as discussed above, recirculated and are typically not more that 100 μm in length on average, preferably not more than 90 μm, more preferably not more than 80 μm in length, and most preferably not more than 75 μm in length. The length of the fines are preferably not more than 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 μm in length, including any and all ranges and subranges therein.

The paper substrate contains from 0.01 to 100 wt % fines, preferably from 0.01 to 50 wt %, most preferably from 0.01 to 15 wt % based upon the total weight of the substrate. The paper substrate contains not mort than 0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 wt % fines based upon the total weight of the paper, including any and all ranges and subranges therein.

The paper substrate may alternatively or overlappingly contain from 0.01 to 100 wt % fines, preferably from 0.01 to 50 wt %, most preferably from 0.01 to 15 wt % based upon the total weight of the fibers contained by the paper substrate. The paper substrate contains not more than 0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 wt % fines based upon the total weight of the fibers contained by the paper substrate, including any and all ranges and subranges therein.

The paper substrate, in one embodiment of the present invention, may contain less fiber “fines” and more long fresh hardwood and/or softwood fibers, preferably virgin. The net affect of the paper substrate is to have a web of cellulose fibers that are more de-bonded than if there were a higher amount of “fines” in the substrate. Utilization of the longer hard long fresh hardwood and/or softwood fibers, preferably virgin, over the fiber fines may result in a less dense sheet containing higher bulk that may be more compressible and uniform resulting in improved smoothness after pressing and/or calendaring. This ideal is demonstrated by Example 1 below combined with FIGS. 1 and 2 show a plot of the Sheffield smoothness, in Sheffield Units (SU), of the ID and NS sides, respectively, of a paper substrate versus the wt % ash contained in that paper substrate. One paper substrate contained highly refined SaveAll pulp with high surface area, while the other contained unrefined pulp. There is a smoother surface at equal ash content for the paper substrates containing the unrefined pulp than those paper substrates containing highly refined and/or recycled and/or SaveAll pulp at the same ash content.

The paper substrate of the present invention may contain a filler.

Fillers may be inorganic. Examples of fillers include, but are not limited to; clay, talc, calcium carbonate, calcium sulfate hemihydrate, and calcium sulfate dehydrate. A preferable filler is calcium carbonate with the preferred form being precipitated calcium carbonate even though it also may in the form of ground calcium carbonate.

The paper substrate of the present invention may contain from 0.001 to 50 wt % of the filler based on the total weight of the substrate, preferably from 0.01 to 40 wt %, most preferably 1 to 30 wt %, of at least one of the filler. This range includes 0.001, 0.002, 0.005, 0.006, 0.008, 0.01, 0.02, 0.03, 0.04, 0.05, 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 4, 5, 6, 8, 10,12, 14, 15, 16, 18, 20, 22, 25, 30, 35, 40, 45 and 50 wt % based on the total weight of the substrate, including any and all ranges and subranges therein.

The paper substrate preferably contains a fiber-filler complex, more preferably a fiber CaCO₃ complex. The fiber-filler is a complex in which the fiber and the filler are engaged in either a chemical and/or physical interaction. Methods of making the fiber-filler complex may be any conventional method, including those described in French Patent 92-04474 and U.S. Pat. Nos. 5,731,080; 5,824,364; 5,679,220; 6,592,712, and 5,665,205, which are hereby incorporated, in their entirety, herein by reference. Further embodiments of making the fiber-filler complex is found in FIGS. 4-6.

The paper substrate preferably contains a fiber-filler complex that is preferably made by the methods described herein. The fiber-filler is a complex in which the fiber and the filler are engaged in either a chemical and/or physical interaction. The ratio of the filler to fiber can be any ratio. The filler/fiber ratio may be from 0.001 to 1000. The filler/fiber ratio may be 0.001, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.5, 3.0, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 225, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, and 1000, including any and all ranges and subranges therein.

The average particle size of the filler when in the fiber filler complex may be any particle size. Examples of the average particle sizes of the filler in the fiber filler complex are those from 0.01 to 20 μm. The average particle size of the filler may be 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.12, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.2, 5.5, 5.7, 6.0, 6.2, 6.5, 6.7, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20, including any and all ranges and subranges therein.

The average surface area of the filler particle in the fiber filler complex may be any particle size. Examples of the surface area of the filler particle in the fiber filler complex are those from 0.1 to 20 m²/g. The surface area of the filler particle in the fiber filler complex may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.12, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.2, 5.5, 5.7, 6.0, 6.2, 6.5, 6.7, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20, including any and all ranges and subranges therein.

The amount of filler attached the fiber in the fiber filler complex may be from 1 to 100 wt % attachment, preferably at least 9 wt % attachment, more preferably at least 15 wt % attachment, most preferably at least 20 wt % attachment based upon the total amount of the filler that is added to the reactor. The amount of filler attached the fiber in the fiber filler complex may be at least 1, 2, 3, 5, 7, 10, 12, 15, 17, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 80, 95, and 99 wt %, including any and all ranges and subranges therein.

The filler is preferably precipitated when in the fiber filler complex. When precipitated, the filler may be of any shape commonly known that precipitated crystals may form. Examples of shapes may be cubic, scalenohdral, rhombic, and/or aragonite. Preferably, the shapes are cubic and/or aragonite.

The paper substrate may contain from 0.1 to 100 wt % fiber filler complex based upon the total weight of the substrate, including 0.1, 0.2, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 wt %, and including any and all ranges and subranges therein.

The fiber filler complex may be made by contacting the fibers, Ca(OH)₂ and/or CO₂ simultaneously and/or consecutively to form a fiber-CaCO3 complex.

The fibers to be added to create the fiber-filler complex may have from 3 to 200 m²/g, including 3, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 125, 150, 175, 200, 225, 250, 275 and 300 m²/g, including any and all ranges and subranges therein.

The fiber-filler complex may be made by adding less than or equal to 5% solids Ca(OH)₂, including less than or equal to 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0% solids Ca(OH)₂ based upon the weight of the reactants, including any and all ranges and subranges therein. However, any % solids of Ca(OH)₂ may be used.

The fiber-filler complex may be made by adding less than or equal to % solids CO₂, including less than or equal to 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0% solids CO₂ based upon the weight of the reactants, including any and all ranges and subranges therein. However, any % solids of CO₂ may be used.

In a preferred embodiment, the fibers are contacted with CO₂

The source of the fibers may be any source. Further, the fibers may be premixed with a gas, liquid, and/or solid carrier such as water, but this is not necessary.

The source of Ca(OH)₂ may be any source. Further, Ca(OH)₂ and/or its source may be in the form of a gas, liquid and/or solid. Still further, the Ca(OH)₂ and/or its source may be premixed with a gas, liquid, and/or solid carrier such as water, but this is not necessary. Preferably, the Ca(OH)2 source may be lime.

The source of CO₂ may be from any source. Further, CO₂ and/or its source may be in the form of a gas, liquid and/or solid. Still further, the CO₂ and/or its source may be premixed with a gas, liquid, and/or solid carrier such as water, but this is not necessary. Preferably, the CO₂ is in the form of a gas and/or liquid.

The CO₂ may be added to the fibers at any time in the process of making the fiber-filler complex. That is, CO₂ may be added to the fibers before the fibers enter the reactor, reaction zone, and/or contact zone. Also, CO₂ may be added to the fibers when the fibers enter the reactor, reaction zone, and/or contact zone.

In one embodiment of the present invention, the fiber-filler complex is made by contacting the fibers with CO₂ prior to contacting the fibers with Ca(OH)₂.

In another embodiment of the present invention, the fiber filler complex is made by mixing, in-line, Ca(OH)₂ in the form of lime with the fibers.

In another embodiment, the fibers are contacted with CO₂, then mixed in-line with Ca(OH)₂ in the form of lime. The fibers and the Ca(OH)₂ in the form of lime form a slurry less than or equal to 5% solids, preferably from 1 to 4% solids, most preferably from 1.5 to 2.5% solids. The % solids of the slurry may include 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 wt %, including any and all ranges and subranges therein.

The fibers, Ca(OH)₂ and/or CO₂ may be contacted together at any pH. Preferably, the pH is greater than or equal to 6, more preferably the pH rnay be from 6 to 12, most preferably from 8 to 10.5. The pH maybe 1, 2, 3, 4, 5, 6, 7, 7.5, 8, 8.5, 8, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, and 14, including any and all ranges and subranges therein.

The fibers, Ca(OH)₂ and/or CO₂ may be contacted together in any manner. Preferably, the contacting occurs in at least one reactor. Examples of reactors include a tubular reactor, a tank reactor, a continuous stirring tank reactor (CSTR), a continuous tubular reactor, and/or plug flow reactor. Preferably, a tubular (plug flow) reactor and/or a series of continuous stirring tank reactors are utilized.

When CO₂ may be further added to the process by adding it at least once to the reactor, a series of CO₂ additions throughout the reactor is also preferable.

When a continuous a tubular (plug flow) reactor is used, it is preferable that a series of CO₂ addition occur throughout the reactor. This embodiment can be seen in FIG. 7.

When a continuous stirring tank reactor is utilized, it is preferable to use multiple continuous stirring tank reactors in series. This embodiment can be seen in FIG. 8.

The reaction conditions may be such so as to promote the fiber and the filler engaged in either a chemical and/or physical interaction.

The method of making the fiber filler complex may be added to any conventional papermaking process. Methods and apparatuses for making paper substrates and paper-related materials are well known in the paper and paperboard art. See for example, G. A. Smook referenced above and references cited therein all of which is hereby incorporated by reference. All such known papermaking methods can be used in the practice of this invention and will not be described in detail. The fiber filler complex may be added to the process in a manner that replaced entirely and/or in part the conventional fibers utilized. The fiber filler complex may be added to the papermaking process in any concentration and/or amount that is desired in order to obtain the desired retention of the fiber filler complex in the paper substrate made therefrom.

The fiber filler complex may be contacted with the paper substrate at any point in the papermaking process. The contacting may occur anytime in the papermaking process including, but not limited to the thick stock, thin stock, head box, size press, water box, and coater. Further addition points include machine chest, stuff box, and suction of the fan pump.

The paper substrate of the present invention may also include optional substances including pigments, dyes, optical brightening agents, fillers not in the form of a fiber-filler complex, retention aids, sizing agents (e.g. AKD and ASA), bindeis, thickeners, and preservatives. Examples of binders include, but are not limited to, polyvinyl alcohol, Amres (a Kyrnene type), Bayer Parez, polychloride emulsion, modified starch such as hydroxyethyl starch, starch, polyacrylamide, modified polyacrylamide, polyol, polyol carbonyl adduct, ethanedial/polyol condensate, polyamide, epichlorohydrin, glyoxal, glyoxal urea, ethanedial, aliphatic polyisocyanate, isocyanate, 1,6 hexamethylene diisocyanate, diisocyanate, polyisocyanate, polyester, polyester resin, polyacrylate, polyacrylate resin, acrylate, and methacrylate. Other optional substances include, but are not limited to silicas such as colloids and/or sols. Examples of silicas include, but are not limited to, sodium silicate and/or borosilicates. Another example of optional substances is solvents including but not limited to water.

The paper substrate of the present invention may contain retention aids selected from the group consisting of coagulation agents, flocculation agents, and entrapment agents dispersed within the bulk and porosity enhancing additives cellulosic fibers.

The paper substrate of the present invention may contain from 0.001 to 50 wt % of the optional substances based on the total weight of the substrate, preferably from 0.01 to 10 wt %, most preferably 0.1 to 5.0 wt %, of each of at least one of the optional substances. This range includes 0.001, 0.002, 0.005, 0.006, 0.008, 0.01, 0.02, 0.03, 0.04, 0.05, 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, 22, 25, 30, 35, 40, 45 and 50 wt % based on the total weight of the substrate, including any and all ranges and subranges therein.

The optional substances may be dispersed throughout the cross section of the paper substrate or may be more concentrated within the interior of the cross section of the paper substrate. Further, other optional substances such as binders for example may be concentrated more highly towards the outer surfaces of the cross section of the paper substrate.

The paper substrate of the present invention may also contain a surface sizing agent such as starch and/or modified and/or functional equivalents thereof at a wt % of from 0.05 wt % to SOwt %, preferably from 5 to 15 wt % based on the total weight of the substrate. The wt % of starch contained by the substrate maybe 0.05, 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, 22, 25, 30, 35, 40, 45 and 20 wt % based on the total weight of the substrate, including any and all ranges and subranges therein. Examples of modified starches include, for exanple, oxidized, cationic, ethylated, hydroethoxylated, etc. Examples of functional equivalents are, but not limited to, polyvinyl alcohol, polyvinylamine, alginate, carboxymethyl cellulose, etc.

The paper substrate may be pressed in a press section containing one or more nips. However, any pressing means commonly known in the art of papermaking may be utilized. The nips may be, but is not limited to, single felted, double felted, roll, and extended nip in the presses. However, any nip commonly known in the art of papermaking may be utilized.

The paper substrate may be dried in a drying section. Any drying means commonly known in the art of papermaking may be utilized. The drying section may include and contain a drying can, cylinder drying, Condebelt drying, IR, or other drying means and mechanisms known in the art. The paper substrate may be dried so as to contain any selected amount of water. Preferably, the substrate is dried to contain less than or equal to 10% water.

The paper substrate may be passed through a size press, where any sizing means commonly known in the art of papermaking is acceptable. The size press, for example, may be a puddle mode size press (e.g. inclined, vertical, horizontal) or metered size press ( e.g. blade metered, rod metered). At the size press, sizing agents such as binders may be contacted with the substrate. Optionally these same sizing agents may be added at the wet end of the papermaking process as needed. After sizing, the paper substrate may or may not be dried again according to the above-mentioned exemplified means and other commonly known drying means in the art of papermaking. The paper substrate may be dried so as to contain any selected amount of water. Preferably, the substrate is dried to contain less than or equal to 10% water.

The paper substrate may be calendered by any commonly known calendaring means in the art of papermaking. More specifically, one could utilize, for example, wet stack calendering, dry stack calendering, steel nip calendaring, hot soft calendaring or extended nip calendering, etc. While not wishing to be bound by theory, it is thought that the presence of the expandable microspheres and/or composition and/or particle of the present invention may reduce and alleviate requirements for harsh calendaring means and environments for certain paper substrates, dependent on the intended use thereof.

The paper substrate may be microfinished according to any microfinishing means commonly known in the art of papermaking. Microfinishing is a means involving frictional processes to finish surfaces of the paper substrate. The paper substrate may be microfinished with or without a calendering means applied thereto consecutively and/or simultaneously. Examples of microfinishing means can be found in United States Published Patent Application 20040123966 and references cited therein, which are all hereby, in their entirety, herein incorporated by reference.

The present invention is explained in more detail with the aid of the following embodiment example which is not intended to limit the scope of the present invention in any manner.

EXAMPLES Example 1

Two paper substrate handsheet sets were made containing varying amounts of ash. Handsheet Set 1 contained SaveAll fiber fines with high surface area, while the other Handsheet Set 2 contained unrefined fibers. FIGS. 1 and 2 show a plot of the Sheffield smoothness, in Sheffield Units (SU), of the ID and NS sides, respectively, of the paper substrates versus the wt % ash contained in that paper substrate. There is a smoother surface at equal ash content for the paper substrates containing the unrefined pulp than those paper substrates containing highly refined and/or recycled and/or SaveAll pulp at the same ash content.

Example 2

A SaveAll fiber fine sample was collected from a mill stream and contained a fluorescence that contributed 46 CIE-Whiteness points. When this sample was mixed with Ca(OH)₂ and then reacted with CO₂ to form CaCO₃ to form a fiber-CaCO₃ complex, the sample contributed 23 CIE-whiteness points, a decrease of 23 CIE-Whiteness points. This decrease in residual OBA efficiency is attributable to quenching of the residual OBA in SaveAll pulp because of the pH increase to >12 when the Ca(OH)₂ is added. The table of FIG. 3 further demonstrates fluorescent data, as measured by CIE-Whiteness, SaveAll fiber fines pulp to the same pulp after forming a fiber-CaCO₃ complex. The addition of Ca(OH)₂ to the fibers caused the pH to increase above 12 and, as the data shows in FIG. 3, caused the residual OBA to become less efficient.

Example 3

The JEP studies that-were targeted for characterizing the fiber-filler complex that is needed to meet the JDA goal (see FIG. 2) will be summarized in this section.

JEP-3: The goal of this study was to identify the best shape and size (i.e., morphology) of the PCC to be attached in a fiber-filler complex in order to maximize bulk and sheet strength. SMI's 4G process was used to produce these samples, with the goal of producing fiber-filler complexes with the PCC component matching the new SMI “3G” products (e.g., Megafil-4000, UltraBulk-II, Albacar-SP, etc.). FIG. 4 summaries the physical test properties of the samples and compares them relative to the Saillat Megafil-2000 (aka, Megafil-S) control sample. As shown in this figure, the UltraBulk-II composite had the best bulk and stiffness opportunity while also reducing the demand for AKD sizing and OBA, relative to Megafil-S. Unfortunately, due to the nature of the “4G” process, which involved pre-carbonating the PCC to >90% conversion before adding fiber, very low attachments of the PCC to the fiber were observed with these samples (see Table-6). As shown in Table-6, the attachment of the UltraBulk-II composite was less than half that of the Carthago tube reactor sample. JEP-4 study began looking at ways to improve the attachment of the PCC to the fiber but most of the advances in this area were done in studies JEP 7-8, which were done in parallel with JEP-7 being done at SMRC's lab and JEP-8 being done in the Easton pilot plant.

JEP-7: The goal of JEP-7 was to explore process variables that impacted the attachment of PCC to fiber, not being concerned with morphology for the present. The samples of JEP-7 were produced using the IP tube located at SMI's Easton pilot plant and the results are summarized in Table-7 and FIG. 5. As shown in Table-7 and FIG. 5, various cubic-shaped products were obtained during this study. These large cubic PCC structures gave better sizing and OBA performance than the Megafil-S control used but also gave slightly lower opacity. The project team believes that this optical deficiency can be overcome with the targeted filler increase. As a result of this study, two process changes were instituted to improve attachment and to try to guide morphology towards the large cubes. These changes are:

(1) Pregasing of the fiber with CO₂ before lime addition. This process change appears to have the effect of improving attachment of the PCC to the fiber.

(2) Performing inline mixing of lime and fiber rather than pre-mixing them before carbonation. This process change appears to direct PCC morphology to a greater tendancy towards cubes.

TABLE 7 Summary of JEP-7 products, showing % attachment, morphology characterization, and carbonating conditions. Note, even though no specific morphology was targeted, large cubic PCC often resulted from the process conditions used. Furthermore, these large cubes were attached well to the fiber. Also in this study it was noted that pre-gassing (i.e., pre-carbonating) the fiber resulted in a greater tendency for large cubic PCC. SAMPLE PRODUCT ATTACHMENT FIBER SCALE OF NUMBER and SIZE (%) REACTOR CONDITION REACTION 4799-61.4 Cubes 43% CSTR and NOT Pre- Pilot Plant 2-5 μm Tube Carbonated 4799-63.1 Cubes 54 CSTR Pre- Pilot Plant 1-2.5 μm Carbonated 4799-79.2 Cubes 61 Tube Pre- Pilot Plant 1-2.5 μm Carbonated 4799-80.1 Cubes 66 CSTR Pre- Pilot Plant 0.5-3 μm Carbonated 4799-81.1 Cubes 28 ? CSTR NOT Pre- Pilot Plant 1.5-2.5 μm Carbonated 4847-143 Cubes 54 CSTR and Pre- Lab 1-2 μm Tube Carbonated

JEP-8: The goal of JEP-8, which was performed in parallel with JEP-7, was to improve upon the attachment of the UltraBulk-II morphology identified in study JEP-3. This work was performed in SMRC using a lab CSTR reactor system. In this study, over fifty experiments were performed testing a range of parameters in an effort to obtain good attachment of the PCC to the fiber while still maintaining the UltraBulk-II morphology identified in study JEP-3. Some of the parameters evaluated include: degree of pre-conversion of PCC before adding fiber, chemical additives, temperature, pressure, reactor type, fiber source, pre-gassing fiber, using various types of seed crystals, etc. In the end, it was concluded that:

(1) Fiber is needed to be present from the start of the reaction in order to achieve good attachment of PCC to the fiber. If the lime was pre-carbonated before adding fiber, it either resulted in poor morphology if the degree of pre-conversion was too low (e.g., <50%) or resulted in poor attachment if the degree of pre-conversion was too high.

(2) When fiber is present from the start of carbonation, morphology control becomes very difficult. In fact, the team was unable to obtain any structure similar to an UltraBulk-II PCC when fiber was present at the start of carbonation. As was in study JEP-7, many of the JEP-8 samples resulted in cubic PCC structures, so it was decided that the team should target and evaluate the cubic fiber-filler complex structures (JEP-9).

Table-8 and FIG. 6 summarize the products and specifications of the JEP-7 products. The handsheet performance of the JEP-7 cubic samples was similar to the cubic samples from JEP-7, in being better performers in terms of AKD and OBA demand, poorer performers optically, and slightly better in bulk (1-3% better). TABLE 8 Summary of JEP-7 products, showing attachment and morphology of the fiber- filler complex, in addition to some process conditions used for its production. SAMPLE PRODUCT ATTACHMENT FIBER NUMBER and SIZE (%) REACTOR CONDITION 4847-23 Amorphous + Cubes 59.7 CSTR NOT Pre- Carbonated 4847-59 Cubes 46.7 Tube and Pre-Carbonated 0.5-1 μm 2 CSTRs 4847-27.2* Aragonite 43.3 CSTR NOT Pre- 1.5-2 μm 97% preconverted Carbonated 4847-94 C Scalenohedral 30.0 Tube NOT Pre- 2 μm Carbonated 4847-167.4B Aragonite 53.6 2 CSTRs NOT Pre- 4 μm 97% preconverted Carbonated

JEP-9: The objective of study JEP-9 was to confirm the performance of cubic fiber-filler composite structures in handsheet paper. The results of JEP-9 were presented to the IP-SMI Executive Committees and the Saillat mill in March 2004. FIG. 7 shows the cubic structures from the JEP-9 study. The DSF handsheet results of the JEP-9 study are summarized in FIGS. 8-14.

Numerous modifications and variations on the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the accompanying claims, the invention may be practiced otherwise than as specifically described herein.

As used throughout, ranges are used as a short hand for describing each and every value that is within the range, including all subranges therein.

All of the references, as well as their cited references, cited herein are hereby incorporated by reference with respect to relative portions related to the subject matter of the present invention and all of its embodiments 

1) A paper substrate, comprising a plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average and having a filler attached thereto a portion of said plurality; less than 50 wt % fibers that are less than 75 μm in length on average based upon the total weight of the substrate. 2) The paper substrate according to claim 1, wherein said plurality of fibers from hardwood species, softwood species are virgin fibers. 3) The paper substrate according to claim 1, wherein said plurality of fibers from hardwood species, softwood species have a Canadian Standard Freeness of from 300 to
 600. 4) The paper substrate according to claim 1, wherein the fibers that are less than 75 μm in length on average are recycled fibers, recirculated fibers, waste fibers, or mixtures thereof. 5) The paper substrate according to claim 1, wherein the filler is attached at a filler to fiber weight ratio of from 0.3 to
 8. 6) The paper substrate according to claim 1, wherein the filler is present in an amount of from 1 to 30 wt % based upon the total weight of the substrate. 7) The paper substrate according to claim 1, comprising from 0.1 to 20 wt % of the fibers that are less than 75 μm in length based upon the total weight of the substrate. 8) The paper substrate according to claim 1, wherein the filler is precipitated calcium carbonate. 9) The paper substrate according to claim 1, wherein the filler is precipitated in at least one shape of selected from the group consisting of cubic, scalenohdral, rhombic, and aragonite. 10) The paper substrate according to claim 9, wherein the filler has an average particle size of from 0.01 to 20 μm. 11) The paper substrate according to claim 9, wherein the filler has an average particle size of from 0.01 to 10 μm. 12) A method of making a paper substrate according to claim 1, comprising contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average and having a filler attached thereto a portion of said plurality with fibers that are less than 75 μm in length on average based upon the total weight of the substrate. 13) The method of claim 12, further comprising contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially. 14) The method of claim 13, further comprising contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average in-line with Ca(OH)₂ to form a slurry having less than 5% solids. 15) The method of claim 13, further comprising contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with CO₂ gas prior to contacting the plurality of fibers with Ca(OH)₂. 16) The method of claim 13, further comprising contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with CO₂ gas prior to contacting the plurality of fibers with Ca(OH)₂. 17) The method of claim 12, further comprising contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially at a pH of from 7.5 to
 11. 18) The method of claim 12, further comprising contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially in a tubular reactor, wherein CO₂ is added to the reactor at multiple addition points. 19) The method of claim 12, further comprising contacting the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially in a series of continuous stirring tank reactor, wherein CO₂ is added to each of the continuous stirring tank reactor in the series. 20) The method of claim 12, further comprising contacting both the plurality of fibers from hardwood species, softwood species or mixtures thereof that are greater than or equal to 75 μm in length on average and the fibers that are less than 75 μm in length on average with Ca(OH)₂ and/or CO₂ simultaneously and/or sequentially in a series of continuous stirring tank reactor, wherein CO₂ is added to each of the continuous stirring tank reactor in the series. 